Laptop continuously shutting off

I have an hp pavillion zx5000. Recently I just beat all of the HL2 series of games on my computer. I had no problems running the game except for minor lag in small amounts of the game. I started to play the original Half Life, and my computer seems to be having the worst time in the world playing the game.

My computer keeps restarting many times when I am looking on the internet now too. It seems to be functioning very slowly, and on the startup after it resets it is moving at grandma speed. I am talking ten minutes to start up and about 15 to shut down. I can't figure out if there is a virus on my computer, I have ran a DXDiag, Ad Aware, and Spybot S&D.

I have 1 gig of ram and I downloaded some quick program off of cnet and found that I have over 300Mb being used up just running normally. I keep my computer very clean, almost to a bare minimum when it comes to startup. Is there any suggestions as to what I need to do or any programs I can use to help me figure out what exactly is my problem right here.

Half Life has been installed on this computer way before these problems. I was just giving that as an example of poor computer performance.

Actually I have fixed the problem with the computer running too hard and fast. It was a power management problem with the settings. I just uninstalled them and restarted my computer.

However, I am still getting these random shut offs. I cannot figure out where they are coming from and why they are doing it. Can someone please help me. The computer is fine now unless it is being used, and it will randomly shut off. It has become more frequent and is having an even harder time starting up. I got some error message once during windows loading, but before I could read it my computer shut off.